Six-mode extended L-band EDFA with a low differential modal gain

We report a numerical investigation on a trench-assisted few-mode erbium-doped fiber amplifier supporting 6 spatial modes with a very low differential modal gain. The numerical investigation is based on the experimentally measured parameters of extended L-band Er 3+ doped fiber. The results show that the differential modal gain of 6 spatial modes covering the spectral range from 1570 to 1616 nm was reduced to as low as 0.28 dB by a mode hybrid core pumped architecture at a 1550 nm pump wavelength. Compared with cladding pumping, our method achieved a gain efficiency increased by 23.1% and a smaller differential modal gain when both average gains reached 20 dB. It is suggested that our investigation shows great potential for decreasing the differential modal gain effectively.